Chinese and Filipino hackers "exchanged fire" in cyberspace over the weekend, adding to the two countries' recent tensions over disputes in the South China Sea.

GMA News Online reported that Filipino "hacktivists" struck back on Saturday at Chinese websites after hackers - "apparently from China" - defaced the official website of the University of the Philippines on Friday.

The news organisation reported that the attack targeted some Chinese sites with calls for sovereignty over the Huangyan and Nansha Islands.The attacks were apparently the work of individuals and were not condoned or encouraged by either government, the report said.

China's Ministry of Foreign Affairs had not issued any comment about the attack by press time on Sunday.

According to Agence France-Presse, hackers claiming to be from China defaced the website of the Philippines' top university on Friday to assert China's claims over the South China Sea.

A screen capture of the defaced site showed a map with Chinese characters that highlighted islands in the South China Sea that are also claimed by the Philippines, said AFP.

"We come from China! Huangyan Island is ours," a caption on the map stated.

Huangyan Island is where the two countries have had vessels stationed for nearly two weeks in a standoff to assert their territorial claims in the area.

A spokesman for the Philippines' Department of Foreign Affairs, Raul Hernandez, suggested the hacking could be linked to the standoff, said AFP.

"These computer hacking(s) are sometimes ... done by some people who are passionately affected and involved in the discussion," he said."We denounce such cyber attacks, regardless of which side they are coming from. They are counter-productive and will only add to the tensions.

"We call on both Filipino and Chinese netizens to be more responsible and encourage dialogue rather than discord," he was quoted as saying by GMA News Online.

The standoff erupted earlier this month when Chinese vessels blocked a Filipino warship from arresting the crews of Chinese fishing boats in the area, which is west of a former United States Navy base at Subic Bay.

China, the Philippines, Vietnam, Malaysia and Brunei all have claims over some islands and waters in the South China Sea, and the US has increased its presence in the Asia-Pacific region, claiming that it has a national interest in the peaceful resolution of disputes in the South China Sea.

US and Filipino troops launched two weeks of annual naval drills on April 16 amid the standoff between China and the Philippines, according to Reuters.

China's Liberation Army Daily warned the US on Saturday that US-Philippine military exercises have raised the risks of an armed confrontation over the South China Sea.